There have been many attempts made at trying to cool a fiber optic bundle exposed to high intensity light sources. The root cause of the heating problem lies in the inefficiency in coupling all of the light energy imparted onto the bundle face into the actual fiber optic strands. A portion of the light is captured in the interstitial zones between adjacently disposed pluralities of fibers. The interstitial zones are created when fiber optic strands having circular cross sections are disposed closely adjacent one another.
The light that enters each interstitial zone within the fiber optic bundle has been determined to be about 9.31% [1-(.pi./(4cos30))] of the light falling on the bundle face. This light becomes absorbed in the cladding of each of the fiber optic strands.
The light falling on the cladding face of the fiber face of each optical fiber strand also does not enter the optical fiber, and therefore also manifests itself as heat. The percentage of loss here is a function of the core/cladding ratio, which varies from manufacturer to manufacturer of the fiber optic strands, and with the diameter of the fiber optic strands. Yet another form of heat generated is light that does enter the fiber face yet is poorly coupled due to a numerical aperture (NA) mismatch from the source to the core medium.
Extensive testing has been performed to better determine exactly where the greatest degree of heat buildup is within the interior of a fiber optic bundle. From this testing it has been determined that the "hot spot" in the bundle is not at the surface as originally believed. The "hot spot" instead manifests itself at a distance from the bundle face according to the three sources of heat described above.
Various attempts have been made to reduce the heat generated within a fiber optic bundle which can cause failure. One attempt has involved trying to reduce the inefficiencies of coupling a light source to a fiber optic bundle by accurate optical methods. Other attempts have involved actually flowing a cooling fluid through a portion of the fiber optic bundle. While possibly providing some degree of heat reduction, these approaches still do not provide the necessary degree of cooling of a fiber optic bundle such that the risk of failure from overheating can be significantly reduced when high intensity light sources are used.
In view of the foregoing, it is a principal object of the present invention to provide a fiber optic bundle construction which much more effectively dissipates the heat developed in the interior areas of the bundle.
It is another object of the present invention to provide a fiber optic bundle construction which makes use of a plurality of heat conductors disposed in the interstitial spaces of the bundle, and wherein the heat conductors are used to conduct heat from the interior areas of the bundle where "hot spots" are often formed.
It is still another object of the present invention to provide a fiber optic bundle construction and method for cooling a fiber optic bundle through the use of a plurality of conductors disposed within the interstitial spaces of the bundle, and wherein the conductors are coupled to a heat sink which assists the conductors in drawing heat generated at the interior areas of the bundle out of the bundle and dissipating same.
It is still another object of the present invention to provide a fiber optic bundle construction and method therefor which allows the interior areas of a fiber optic bundle to be cooled through the use of a plurality of conductors disposed in the interstitial spaces of the bundle, where the conductors do not significantly complicate the construction of the fiber optic bundle or add significantly to its overall cost.